Molecular associations between and among purines, pyrimidines and amino acids are of paramount importance in determining the organization of life processes. Similar associations involving coenzymes such as NAD ion and FAD may be essential in some of the biochemical oxidation-reduction reactions that these molecules undergo. It is proposed to elucidate the nature of the molecular associations of the above substances by means of single crystal X-ray diffraction studies. In most cases this will be done through the analysis of synthetic model compounds due to the difficulty of crystallizing the compounds or complexes of direct interest. In particular, the nature of the following phenomena will be studied: (a) Interactions between nucleic acid bases, especially those between non-Watson-Crick base pairs. (b) Intramolecular interactions in the redox coenzymes NAD ion and FAD in their various oxidation states and intermolecular interactions between nicotinamide and isoalloxazine rings. (c) Protein-nucleic acid interactions. (d) Interaction between proteins and the coenzymes NAD ion and FAD. The information thereby elucidated should significantly further our understanding of how proteins, nucleic acids and redox coenzymes associate at the molecular level.